The present invention relates to a continuous, chemical vapor deposition (CVD) method for producing a coated glass article, particularly, coated architectural glass or automotive glass. Specifically, the invention relates to an improved method for producing a glass article coated with a layer of zinc oxide.
Zinc oxide films have previously been described in the patent literature.
U.S. Pat. No. 4,751,149 describes deposition of zinc oxide films by a chemical vapor deposition (CVD) process for use in photovoltaic devices. The process described introduces an organozinc compound, an oxidant and an inert carrier gas into a chamber containing a substrate heated to a temperature in the range of 60° C. to 350° C. The films formed are said to contain hydrogen and may be modified to contain a Group XIII element by introducing volatile Group XIII compounds into the chamber along with the organozinc compound and oxidant.
U.S. Pat. No. 5,002,796 describes a functional zinc oxide thin film having high light permeability and low resistivity which can be obtained at a low temperature of about 200° C. on an inexpensive substrate such as glass by a method of activating a starting material gas by means of activation energy, in a space different from a film-forming space thereby forming a precursor contributing to the formation of a deposited film, activating a starting material gas in a space different from the film-forming space and the space just-mentioned above by means of activation energy thereby forming an active species that chemically reacts with the precursor, and introducing the precursor and the active species into the film-forming space, thereby depositing a film, wherein the starting material gas for forming the precursor is an alkyl zinc compound and the starting material for forming the active species is an oxygen gas or an ozone gas. This enables mass production of photovoltaic devices at high efficiency using a PN junction or PIN junction or high performance flat display device using liquid crystals, by which practical provision of power sources for domestic equipments or power sources for electric power appliance or large area display device can be obtained at a reduced cost.
Zinc oxide films have also previously been described in the non-patent, scientific literature.
Shealy, James R. et al., “Preparation and Properties of Zinc Oxide Films Grown by the Oxidation of Diethylzinc”, Journal of the Electrochemical Society, Vol. 128, No. 3, (1981), pg. 558-561, describes the preparation and properties of zinc oxide films grown by the oxidation of diethylzinc. Growth above 250° C. with an oxygen to diethylzinc mole ratio in excess of 10 is said to result in stable films of zinc oxide, free from carbon contamination or zinc-ethyl groups. Details are provided of these growth conditions and also of the resulting growth parameters in this paper. The physical properties of films grown by this technique are also described, with particular emphasis on their IR absorption characteristics, stoichiometry, refractive index, and crystallographic orientation as a function of the growth conditions. Films are shown to have an oxygen deficiency, which increases with growth temperature, as does their refractive index. Film orientation, along the c-axis, is also found to improve with increasing growth temperatures.
Roth, A. P. and Williams, D. F., “Properties of Zinc Oxide Films Prepared by the Oxidation of Diethylzinc”, Journal of Applied Physics, Vol. 52, No. 11 (1981), pg. 6685-6692, describes polycrystalline transparent semiconducting zinc oxide films deposited by the oxidation of diethylzinc. The film growth rate is controlled by a complex multistep oxidation process, which is dominated by radical reactions. Samples deposited between 280 and 350° C. have a conductivity varying from 10−2 to 50 Ω−1 cm−1. The electrical properties of the films which are typical of polycrystalline material with small crystallites are shown to depend very closely on the film growth conditions. A study of oxygen chemisorption at grain boundaries confirms the importance of grain boundary effects in ZnO polycrystalline films.
Li, X. et al., “P-Type ZnO Thin Films Formed by CVD Reaction of Diethylzinc and NO Gas”, Electrochemical and Solid-State Letters”, Vol 6, No. 4 (2003) pg. C56-C58, discusses the use of nitric oxide (NO) gas to dope ZnO p-type films, fabricated using metallorganic chemical vapor deposition (CVD) reaction of a Zn metallorganic precursor and NO gas. NO gas is used to supply both O and N to form a N-doped ZnO (ZnO:N) film. Auger electron spectroscopy analysis indicated that, under Zn-rich conditions, the N concentration in the film is readily detectable, with the highest concentration being ˜3 atom %. For concentrations greater than 2 atom %, the films are p-type. The carrier concentration varies from 1.0×1015 to 1.0×1018 cm−3 and the mobility is approximately 10−1 cm2 V−1. The minimum film resistivity achieved is ˜20 ohm-cm.
Known processes for the production of zinc oxide layers on a substrate are limited in the thickness or number of the films formed given the low efficiency of the known deposition processes, and also by powder formation (pre-reaction) of the reactive elements. Therefore, it is desired to devise an improved process for the formation of zinc oxide coatings on a substrate.